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Behold ATLAS, the Holder of the Heavens! (My Summit Build)

Behold ATLAS, the Holder of the Heavens! (My Summit Build)

Have wanted a Summit since it first came out 3 years ago… Finally, got a new green Summit in April 2012. Had a short list of modifications that I knew I wanted to do, so this thread will document some of those mods, as well as give fun ideas for others, hopefully!

Here's a vid of the beast in action.

(All of my RCs have names. This Summit is named "ATLAS" after the Titan who holds the sky on his shoulders, because he's big and strong, just like my Summit!)

I'll be posting a new post for each section of the mods, so I can include pics and not run over the 10 pic limit per post.

Radio / Receiver Mods

Radio setup:
Promptly sold the Tqi radio and got a TQ Link, as I prefer the feel and look of the old radios.

Switches:

Stock 3-position switch – Used a y-splitter to combine functions of High/Low tranny shifter and the lockers:
Position 1: HIGH gear, all diffs UNLOCKED
Position 2: LOW gear, all diffs UNLOCKED
Position 3: LOW gear, all diffs LOCKED

Power Setup

Motor: Stock 775 titan
ESC: Stock EVX-2

Batteries: 2x 6000mah China Hadrcase 2S lipos – these things last forever! Super tight squeeze into the battery trays. You couldn’t possibly get a taller battery in the trays (longer yes, but taller no). Had to mod the battery vents to allow connector to come out there.

7.2V 4.5A UBEC driving all lights and servos (2-5S rated, running it on 4S so both batts get drained evenly.) This works perfectly, too. My batts always come out after a run only .01-.02V apart in voltage. That gives me maximum runtime on any set of batteries.

(soldered the connectors for the UBEC directly to the batt connectors on ESC.)

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Is 7.2V safe for the servos and electronics? Definitely – all of Traxxas servos and electronics (rx, etc.) are designed to run on 6.0V, in fact they are “rated” to run at 6.0V, which means that they are design to run on a 5-cell nimh/nicad rx pack. 6.0V is the nominal rating (1.2V * 5) for 5 nickel-based cells. The actual *charged* voltage for a 5-cell pack is 1.4V * 5, or even 1.5V * 5 fresh off the charger, which gives you between 7.0 and 7.5 *actual* volts. So, the 7.2V BEC falls right within this range of voltage that the rx and servos must be able to deal with, since they are rated for 5 cells of nimh/nicad.

The only other consideration of operating at 7.2V is the LEDS. Traxxas does not use any resistors, and uses series circuits to split up the voltage between LEDS in the circuit. (e.g. 6.0V from the BEC is split up between two white LEDs, so each sees 3.0. Likewise, 6.0V is split up between 3 red LEDS, so each sees 2.0V)
Now, White LEDS are rated typically between 3.0 and 3.7V, while Red LEDS are typically rated between 2.0 and 2.3V. So, you can see that running at 7.2V will push the White LEDS at 3.6V each (still within spec, though much higher up in it), and the reds gets pushed past the limit at 2.4V (which results in them running a bit hot, and they seem to die after several weeks at this higher voltage. I've since added a 4th red LED to each side of the rear bumper, so each is at 1.8V - perfect)

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FYI: My testing confirmed the following info: Traxxas LVC still works even if you are not using the built-in BEC in the EVX-2. Also, the built-in LVC kicks in at exactly 3.5V per cell (or total pack voltage of 7.0V). This is when under load, so if you’ve got a high-drain scenario (high gear bashing), the resting voltage will be much higher (3.7-3.8V). But in low-gear, the drain is much lower, so you should definitely stop driving once it kicks in in low gear.

Steering

2x Solar D772 servos, rated for ~400in-lbs of torque @ 7.2V, but probably 250-300 is more like it. Packed them with grease to help with "waterproofing".

They seem overrated to me, but definitely stronger than stock, and slightly slower (though the higher voltage of 7.2V BEC helps them move at a closer speed to the 2075s than the stock 6.0V output from the EVX-2)

Had to tighten up the servo-saver with two washers – still has a little give, but allows more power from the servos to reach the wheels before it “slips”.

Much more amp draw – These pushed the EVX-2 BEC to its limit (lights would fliker noticeably on switching direction of the servo). Much better with the 7.2V 4.5A BEC (lights do not “flicker” nearly so much when doing quick servo reversals for max amp draw). My guess is that these servos draw about 1 amp peak each.

The servos fit great, but you can't use the traxxas horns - gotta use the Solar horns, and cut one end off with knife or dremel.

By having several strips of different lengths, I can "stack" the weights inside the wheel, for fine-tuning how much weight is in the front. (Though, I usually just leave all of it in - max forward grip, since I mostly just crawl with this thing.)

Had to screw three screws into wheels to hold the removable weights in place when truck tilts or lands on its side.) Part of the design goal was to come up with a way to keep the weights removable/replaceable without having to take the wheels off the car. Works great, btw!

Here is a vid of how it works (took the wheel off the car, to maximize visibility, but you can imagine how it could be done with the wheels on the car):

With just the first strip (17 pcs x .25oz) of weights: 4.25oz on each wheel (8.5 oz, or 1/2 lb total)
Add the second strip (15 pcs x .25oz) of weights: 8oz on each wheel (16 oz, or 1 lb total)
Add the third strip (13 pcs x .25oz) of weights: 11.25oz on each wheel (22.5 oz, or nearly 1.5 lbs total!)

They stay great in the wheels - I've never had one come out or even come loose.